Sweep voltage generator



May 23, 1950 ZAGOR 2,508,879

SWEEP VOLTAGE GENERATOR Filed Nov. 27, 1944 Al L INVENTOR. HERBERT I. ZAGOR ATTORNEY lar wave gate circuit including triodes l and II, a sweep voltage generator including diode l2 and pentode l3 and an inverter stage including triode l4. Plate voltage for tubes ID to I4 is furnished by a battery IS.

The rectangular wave generator is of conventional design, the output wave being initiated by a negative triggering pulse l6 applied to input terminals ll. A voltage divider I8, controlling the grid bias of triode I0, is adjusted so that this tube is normally conductive. The application of a negative triggering pulse to the grid of triode l0 renders the tube non-conductive thereby imposing a positive pulse through resistor I9 on the grid of triode H, rendering same conductive. The resultant IR drop in resistor 20 reduces the voltage on the plate of triode H, but since the voltage of condenser 2| cannot change instantaneously the grid voltage of triode I 0 is lowered by an amount that is initially equal to the reduction of plate voltage .on triode H- and current continues to flow in triode II. The drop in voltage across resistor 20, however, causes the current to flow into condenser 2| through resistor 22 and thus raise the grid voltage of triode Ill. After a time interval that is determined by the magnitude of the time constant of resistor 22 and condenser 2| and to a lesser degree by the values of resistor 20 and the supply voltage, the grid voltage of triode l0 attains 'the value at which the current again triggers to render triode ll non-conductive. If the resistor 20 is sufiiciently small in comparison with resistor 22 so that the current flow in condenser 2! does not greatly affect the IR drop in resistor 20., the voltage pulse developed across resistor 20 is rectangular in form. The length of this pulse may be controlled by varying resistor 22. Accordingly, for each triggering pulse applied to terminals 11 there is produced a rectangular pulse 23 which is taken off the plate of triode II.

The rectangular pulses 23 are applied through a coupling capacitor 24 to the suppressor grid of pentode l3. Diode l2, having its plate connected to the suppressor grid and its cathode to ground, serves to maintain the voltage on the suppressor grid at zero level or below, since if the applied gate voltage goes positive, the diode conducts to ground. Thus the voltage applied to the suppressor of pentode I3 assumes the form shown in Figure 2A where it will be seen that the voltage for the duration of the gating pulses is at zero potential, (zero level is indicated by the dashed line) and at a highly negative potential in the interim between gating pulses.

The operation of pentode l3 will now be discussed commencing with the condition existing prior to the application of a gating pulse to the suppressor grid thereof. Since a highly negative bias is now impressed on the suppressor grid,

pentode I3 is non-conductive and condenser 25 connected between the plate and grid is fully charged to the plate voltage. When the gating pulse is applied pentode l 3 is rendered conductive permitting condenser 25 to discharge therethrough in series with variable resistor 28. The discharge current flowing through resistor 28 develops a voltage drop thereacross which applies a negative bias to the grid as shown by Figure 23. It will be seen that this bias assumes a definite value for the duration of the gating pulse, the discharge current flow being regulated by the varying impedance of pentode l3.

The screen grid-o! pentode l3 obtains its potential from a tap position along a voltage divider 21 shunted across the power supply IS. A condenser '28 is connected between the tap on divider 21 and ground, the value of said condenser being such as to partially by-pass the screen grid. As a result, when pentode I3 is rendered conductive by the gating pulse the flow of screen current is such as to cause a rise in screen voltage in accordance with curve shown in Figure 2C. It may then be seen that inasmuch as the control grid voltage for the duration of the gating pulse is constant and the screen grid voltage is variable, the resultant variation in plate current will be a function of screen voltage and, in this case, for reasons to be further explained, will assume a linear sawtooth pattern.

Referring now to Figure 3, the influence of screen voltage upon plate voltage in pentode I3 is illustrated. Since as screen voltage rises the resultant current flow through plate resistor 29 reduces the voltage on the plate of pentode IS, the screen and plate voltages are out of phase. Thus if the screen voltage Es were to rise in a linear manner, the plate voltage Ep would fall in a curved linein accordance with the characteristic of the pentode. However, since the voltage on the screen rises in accordance with the curve shown in Figure 20, which curve is substantially identical with the curve taken by plate voltage E1: in the instance of a linear rise in screen voltage Ep in Figure 3, the overall effect is to cause the plate voltage to fall linearly. This condition is indicated in Figure 3 by the dashed lines.

When the tube is rendered non-conductive in the interim between gating pulses, the suppressor grid is again biased beyond cut-off causing the plate voltage on pentode l3 to fall abruptly, thereby completing the sawtooth wave. The voltage on the plate of pentode l3, therefore, assumes the wave pattern shown in Figure 2D, wherein the dashed line represents voltage level prior to the application of the gating pulse.

The negative going sawtooth wave 30 is then applied to the grid of an inverter tube I 4 through condenser 3|. The voltage on the plate of triode I4, being 180 out of phase with the grid voltage, assumes the form of a positive going sawtooth wave 32 which is applied to the horizontal deflect'ion plates of a cathode ray tube 33 through a coupling capacitor 34. Inasmuch as the sawtooth voltages applied to the grid of inverter tube II are of high amplitude, negative feed back is provided by a capacitor 35 connected between grid and plate for the purpose of maintaining linear amplification.

While there has been described what is at present considered a preferred embodiment of the invention, it will be manifest to those skilled in the art that various changes and modifications may be made therein without departing from the invention and it is therefore aimed in the appended claims to cover all such changes and modifications as fall Within the spirit and scope of the invention.

What is claimed is:

1. A sawtooth voltage generating circuit comprising an electron discharge device having at least an anode, a cathode, a control grid, a screen grid and a suppressor grid, a source of direct potential connected thru a first impedance to said anode and thru a second impedance to said screen grid, means for applying an input rectangular wave to said suppressor grid to bias said discharge device to cut-off except during the positive portion of said wave including a resistance capacitance coupling circuit and a diode shunting said resistance, means responsive to the conduction of said tube for applying a steady bias to said control grid and means responsive to the conduction of said tube to cause the voltage on said screen grid to vary exponentially thereby causing the current thru said first impedance to increase ata linear rate.

2. A sawtooth voltage generating circuit comprising an electron discharge device having at least an anode, a cathode, a control grid, a screen grid and a suppressor grid, a source of direct potential connected thru an impedance to said anode, a potentiometer connected across said source of potential, the adjustable arm of said potentiometer being connected to said screen grid, means for applying an input rectangular wave to said suppressor grid to bias said discharge device to cut-01f except during the positive pord tion of said wave including a resistance capacitance coupling circuit and a diode shunting said resistance, means responsive to the conduction of said tube for applying a steady bias to said control grid, and means for partially by-passing said screen grid comprising a capacitor connected between said screen grid and one side of said source of potential whereby the screen grid voltage varies exponentially thereby causing the current thru said first impedance to increase at a linear rate.

HERBERT I. ZAGOR.

REFERENCES CITED UNITED STATES PATENTS Name Date Young Sept. 12, 1939 Number 

